Dipeptidase-inactivated tACE action in vivo: selective inhibition of sperm-zona pellucida binding in the mouse

Target silencing of porcine SPAG6 and PPP1CC by shRNA attenuated sperm motility

The quality of sperm significantly influences the reproductive efficiency of pig herds. High-quality sperm is necessary for efficient fertilization and to maximize the litter numbers in commercial pig farming. However, the understanding of genes regulating porcine sperm motility and viability is limited. In this study, we validated porcine sperm/Sertoli-specific promoters through the luciferase reporter system and identified vital genes for sperm quality via loss-of-function means. Further, the shRNAs driven by the ACE and SP-10 promoters were used to knockdown the SPAG6 and PPP1CC genes which were provisionally important for sperm quality. We assessed the effects of SPAG6 and PPP1CC knockdown on sperm motility by using the sperm quality analyzer and flow cytometry. The results showed that the ACE promoter is active in both porcine Sertoli cells and sperms, whereas the SP-10 promoter is operating exclusively in sperm cells. Targeted interference with SPAG6 and PPP1CC expression in sperm cells decreases the motility and increases apoptosis rates in porcine sperms. These findings not only offer new genetic tools for targeting male germ cells but also highlight the crucial roles of SPAG6 and PPP1CC in porcine sperm function.

Localization and Distribution of Testicular Angiotensin I Converting Enzyme (ACE) in Neck and Mid-Piece of Spermatozoa from Infertile Men in Relation to Sperm Motility

Testicular angiotensin converting enzyme (ACE) is known to play an essential role in the male reproduction and fertility. Data about tACE in cases of male infertility are quite scarce, and in this respect we aimed to study localization and distribution of tACE protein in the neck and mid-piece of spermatozoa from pathological samples in relation to sperm motility. The enzyme expression during capacitation and acrosome reaction was quantitatively assessed. In human ejaculated spermatozoa tACE is localized on sperm plasma membrane of the head, the neck and mid-piece of the tail. The immunoreactivity becomes stronger in capacitated spermatozoa followed by a decrease in acrosome reacted sperm. In different cases of semen pathology (oligozoospermia, asthenozoospermia and teratozoospermia) fluorescent signals in the neck and mid-piece are in punctate manner whereas in normozoospermia they were uniformly distributed. The expression area of tACE the neck and mid-piece was decreased in ejaculated and capacitated sperm from pathological semen samples compared to normospermia. Significant positive correlation was established between tACE area and progressive sperm motility, whereas with immotile sperm the correlation was negative. Our data suggest that proper distribution of tACE in the neck and mid-piece is required for normal sperm motility that could be used as a novel biomarker for male infertility.

Dissecting the PRSS37 interactome and potential mechanisms leading to ADAM3 loss in PRSS37-null sperm

A disintegrin and metalloproteinase 3 (ADAM3) is a sperm membrane protein critical for sperm migration from the uterus into the oviduct and sperm-egg binding in mice. Disruption of PRSS37 results in male infertility concurrent with the absence of mature ADAM3 from cauda epididymal sperm. However, how PRSS37 modulates ADAM3 maturation remains largely unclear. Here, we determine the PRSS37 interactome by GFP immunoprecipitation coupled with mass spectrometry in PRSS37-EGFP knock-in mice. Three molecular chaperones (CLGN, CALR3 and PDILT) and three ADAM proteins (ADAM2, ADAM6B and ADAM4) were identified to be interacting with PRSS37. Coincidently, five of them (except ADAM4) have been reported to interact with ADAM3 precursor and regulate its maturation. We further demonstrated that PRSS37 also interacts directly with ADAM3 precursor and its deficiency impedes the association between PDILT and ADAM3. This could contribute to improper translocation of ADAM3 to the germ cell surface, leading to ADAM3 loss in PRSS37-null mature sperm. The understanding of the maturation mechanisms of pivotal sperm plasma membrane proteins will pave the way toward novel strategies for contraception and the treatment of unexplained male infertility.

Physiological implications of COVID-19 in reproduction: angiotensin-converting enzyme 2 a key player

The COVID-19 outbreak, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), was first identified in China, and it has quickly become a global threat to public health due to its rapid rate of transmission and fatalities. Angiotensin-converting enzyme 2 (ACE2) has been identified as a receptor that mediates the entry of SARS-CoV-2 into human cells, as in the case of severe acute respiratory syndrome coronavirus (SARS-CoV). Several studies have reported that ACE2 expression is higher in Leydig, Sertoli and seminiferous ductal cells of males, as well as in ovarian follicle cells of females, suggesting possible potential pathogenicity of the coronavirus in the reproductive system. Higher ACE2 expression in the human placenta and reports of vertical transmission of SARS-CoV-2 among clinical cases have increased the relevance of further studies in this area. This review focuses on the interaction between SARS-CoV-2 and the ACE2 receptor and speculates on the mechanistic interplay in association with male and female reproductive physiology. In addition, based on the available literature, we discuss the alleged sex differences in terms of the infectivity of SARS-CoV-2, which is claimed greater among males, and further explore the physiological role of ACE2 and 17β-oestradiol for the same.

Dephosphorylation of protamine 2 at serine 56 is crucial for murine sperm maturation in vivo

The posttranslational modification of histones is crucial in spermatogenesis, as in other tissues; however, during spermiogenesis, histones are replaced with protamines, which are critical for the tight packaging of the DNA in sperm cells. Protamines are also posttranslationally modified by phosphorylation and dephosphorylation, which prompted our investigation of the underlying mechanisms and biological consequences of their regulation. On the basis of a screen that implicated the heat shock protein Hspa4l in spermatogenesis, we generated mice deficient in Hspa4l (Hspa4l-null mice), which showed male infertility and the malformation of sperm heads. These phenotypes are similar to those of Ppp1cc-deficient mice, and we found that the amount of a testis- and sperm-specific isoform of the Ppp1cc phosphatase (Ppp1cc2) in the chromatin-binding fraction was substantially less in Hspa4l-null spermatozoa than that in those of wild-type mice. We further showed that Ppp1cc2 was a substrate of the chaperones Hsc70 and Hsp70 and that Hspa4l enhanced the release of Ppp1cc2 from these complexes, enabling the freed Ppp1cc2 to localize to chromatin. Pull-down and in vitro phosphatase assays suggested the dephosphorylation of protamine 2 at serine 56 (Prm2 Ser⁵⁶) by Ppp1cc2. To confirm the biological importance of Prm2 Ser⁵⁶ dephosphorylation, we mutated Ser⁵⁶ to alanine in Prm2 (Prm2 S56A). Introduction of this mutation to Hspa4l-null mice (Hspa4l ^-/-; Prm2 ^S56A/S56A) restored the malformation of sperm heads and the infertility of Hspa4l ^-/- mice. The dephosphorylation signal to eliminate phosphate was crucial, and these results unveiled the mechanism and biological relevance of the dephosphorylation of Prm2 for sperm maturation in vivo.

Angiotensin converting enzymes in fish venom

Animal venoms are multifaceted mixtures, including proteins, peptides and enzymes produced by animals in defense, predation and digestion. These molecules have been investigated concerning their molecular mechanisms associated and possible pharmacological applications. Thalassophryne nattereri is a small venomous fish inhabiting the northern and northeastern coast of Brazil, and represents a relatively frequent cause of injuries. Its venom causes severe inflammatory response followed frequently by the necrosis of the affected area. Scorpaena plumieri is the most venomous fish in the Brazilian fauna and is responsible for relatively frequent accidents involving anglers and bathers. In humans, its venom causes edema, erythema, ecchymoses, nausea, vomiting, and syncope. Recently, the presence of a type of angiotensin converting enzyme (ACE) activity in the venom of Thalassophryne nattereri and Scorpaena plumieri, endemic fishes in northeastern coast of Brazil, has been described. The ACE converts angiotensin I (Ang I) into angiotensin II (Ang II) and inactivates bradykinin, there by regulating blood pressure and electrolyte homeostasis, however, their function in these venoms remains an unknown. This article provides an overview of the current knowledge on ACE in the venoms of Thalassophryne nattereri and Scorpaena plumier.

Testis-specific isoform of angiotensin-converting enzyme (tACE) is involved in the regulation of bovine sperm capacitation

We hypothesized that the testis-specific isoform of angiotensin-converting enzyme (tACE) is released during bovine sperm capacitation, and its peptidase activity is required for capacitation. Specific objectives of this study were to (i) develop an anti-tACE antibody; (ii) characterize expression of tACE in bovine testes and sperm; and (iii) determine the role of tACE in capacitation. A 110-kDa protein, consistent with the mass of tACE, was detected in sperm extract by our anti-tACE immunoserum. This immunotarget localized at the acrosomal region and principal piece, but was only expressed in testis of mature bulls. When bull sperm were incubated in Sp-TALP (0 and 4 hr) plus 10 µg/ml heparin (capacitation group) or 10 µg/ml heparin + 10 µM captopril (an ACE inhibitor) for 4 hr, the number of acrosome-reacted (40.1 vs. 24.0%, respectively) and hyperactivated (15.0 vs. 9.7%) sperm increased, and tyrosine phosphoprotein content were higher (p < 0.05) for sperm in heparin alone. tACE activity was also higher (0.04 U/ml; p < 0.01) in incubation medium of sperm exposed to heparin compared to 0- and 4-hr incubation controls or heparin + captopril conditions (0, 0.005, and 0.009 U/ml, respectively). Furthermore, capacitation-associated shedding of a portion of tACE into the medium decreased sperm content of the 110-kDa tACE, but concurrently increased the abundance of a 60-kDa tACE variant. Thus, a portion of the extracellular region of tACE (containing its catalytic site) is released from bovine sperm during capacitation, and tACE activity may be required for sperm capacitation.

A bradykinin-potentiating peptide (BPP-10c) from Bothrops jararaca induces changes in seminiferous tubules

Background

The testis-specific isoform of angiotensin-converting enzyme (tACE) is exclusively expressed in germ cells during spermatogenesis. Although the exact role of tACE in male fertility is unknown, it clearly plays a critical function in spermatogenesis. The dipeptidase domain of tACE is identical to the C-terminal catalytic domain of somatic ACE (sACE). Bradykinin potentiating peptides (BPPs) from snake venoms are the first natural sACE inhibitors described and their structure–activity relationship studies were the basis for the development of antihypertensive drugs such as captopril. In recent years, it has been showed that a number of BPPs – including BPP-10c – are able to distinguish between the N- and C-active sites of sACE, what is not applicable to captopril. Considering the similarity between tACE and sACE (and since BPPs are able to distinguish between the two active sites of sACE), the effects of the BPP-10c and captopril on the structure and function of the seminiferous epithelium were characterized in the present study. BPP-10c and captopril were administered in male Swiss mice by intraperitoneal injection (4.7 μmol/kg for 15 days) and histological sections of testes were analyzed. Classification of seminiferous tubules and stage analysis were carried out for quantitative evaluation of germ cells of the seminiferous epithelium. The blood-testis barrier (BTB) permeability and distribution of claudin-1 in the seminiferous epithelium were analyzed by hypertonic fixative method and immunohistochemical analyses of testes, respectively.

Results

The morphology of seminiferous tubules from animals treated with BPP-10c showed an intense disruption of the epithelium, presence of atypical multinucleated cells in the lumen and degenerated germ cells in the adluminal compartment. BPP-10c led to an increase in the number of round spermatids and total support capacity of Sertoli cell in stages I, V, VII/VIII of the seminiferous epithelium cycle, without affecting BTB permeability and the distribution of claudin-1 in the seminiferous epithelium. Interestingly, no morphological or morphometric alterations were observed in animals treated with captopril.

Conclusions

The major finding of the present study was that BPP-10c, and not captopril, modifies spermatogenesis by causing hyperplasia of round spermatids in stages I, V, and VII/VIII of the spermatogenic cycle.

Angiotensin-converting enzymes play a dominant role in fertility

According to the World Health Organization, infertility, associated with metabolic syndrome, has become a global issue with a 10%–20% incidence worldwide. An accumulating body of evidence has shown that the renin–angiotensin system is involved in the fertility problems observed in some populations. Moreover, alterations in the expression of angiotensin-converting enzyme-1, angiotensin-converting enzyme-2, and angiotensin-converting enzyme-3 might be one of the most important mechanisms underlying both female and male infertility. However, as a pseudogene in humans, further studies are needed to explore whether the abnormal angiotensin-converting enzyme-3 gene could result in the problems of human reproduction. In this review, the relationship between angiotensin-converting enzymes and fertile ability is summarized, and a new procedure for the treatment of infertility is discussed.

Evolution of genes involved in gamete interaction: evidence for positive selection, duplications and losses in vertebrates

Genes encoding proteins involved in sperm-egg interaction and fertilization exhibit a particularly fast evolution and may participate in prezygotic species isolation [1], [2]. Some of them (ZP3, ADAM1, ADAM2, ACR and CD9) have individually been shown to evolve under positive selection [3], [4], suggesting a role of positive Darwinian selection on sperm-egg interaction. However, the genes involved in this biological function have not been systematically and exhaustively studied with an evolutionary perspective, in particular across vertebrates with internal and external fertilization. Here we show that 33 genes among the 69 that have been experimentally shown to be involved in fertilization in at least one taxon in vertebrates are under positive selection. Moreover, we identified 17 pseudogenes and 39 genes that have at least one duplicate in one species. For 15 genes, we found neither positive selection, nor gene copies or pseudogenes. Genes of teleosts, especially genes involved in sperm-oolemma fusion, appear to be more frequently under positive selection than genes of birds and eutherians. In contrast, pseudogenization, gene loss and gene gain are more frequent in eutherians. Thus, each of the 19 studied vertebrate species exhibits a unique signature characterized by gene gain and loss, as well as position of amino acids under positive selection. Reflecting these clade-specific signatures, teleosts and eutherian mammals are recovered as clades in a parsimony analysis. Interestingly the same analysis places Xenopus apart from teleosts, with which it shares the primitive external fertilization, and locates it along with amniotes (which share internal fertilization), suggesting that external or internal environmental conditions of germ cell interaction may not be the unique factors that drive the evolution of fertilization genes. Our work should improve our understanding of the fertilization process and on the establishment of reproductive barriers, for example by offering new leads for experiments on genes identified as positively selected.

Characterization and activity of angiotensin-converting enzyme in Holstein semen

The study was designed to perform immunodetection in spermatozoa and seminal plasma, immunolocalization in spermatozoa, and evaluation of the enzymatic activity of angiotensin-converting enzyme (ACE) in the semen of Holstein bulls. We used ejaculates from five bulls as part of a regular collection of semen. The monoclonal anti-ACE antibody recognized a single protein band with 100 kDa in detergent extract prepared from sperm and in seminal plasma. ACE enzymatic activity in sperm was 43.7, 21.3, 45.6, 60.0, and 57.7 mU/mL in bulls 1, 2, 3, 4, and 5, respectively, and 0.3, 2.3, 3.0, 2.3, and 2.6 mU/mL in seminal plasma of the same bulls, respectively. The average percentages of sperm with acrosome reactions after treatment with heparin were 28.3%, 28.6%, 35.2%, 25.0%, and 32.3%, respectively. These values were higher than the percentages of acrosome reactions in controls and the captopril group (P<0.05), although no difference was seen between the captopril and control groups (P>0.05). After 4h of incubation, motility in the control group (32.9%) was significantly higher than that in the heparin (15.7%) and captopril (12.1%) groups. No difference was found in motility after the capacitation assay in the heparin and captopril groups (P>0.05). In conclusion, ACE was immunologically localized in the acrosome of the spermatozoa of Holstein bull, the specific enzymatic activity of ACE in detergent-extracted spermatozoa and seminal plasma was inhibited by captopril, and this ACE inhibitor reduced the percentage of sperm with progressive motility and acrosome reactions after capacitation in vitro.

Protein disulfide isomerase homolog PDILT is required for quality control of sperm membrane protein ADAM3 and male fertility [corrected]

A disintegrin and metalloproteinase 3 (ADAM3) is a sperm membrane protein critical for both sperm migration from the uterus into the oviduct and sperm primary binding to the zona pellucida (ZP). Here we show that the testis-specific protein disulfide isomerase homolog (PDILT) cooperates with the testis-specific calreticulin-like chaperone, calsperin (CALR3), in the endoplasmic reticulum and plays an indispensable role in the disulfide-bond formation and folding of ADAM3. Pdilt(-/-) mice were male infertile because ADAM3 could not be folded properly and transported to the sperm surface without the PDILT/CALR3 complex. Peculiarly we find that not only Pdilt(-/-), but also Adam3(-/-), spermatozoa effectively fertilize eggs when the eggs are surrounded in cumulus oophorus. These findings reveal that ADAM3 requires testis-specific private chaperones to be folded properly and that the principle role of ADAM3 is for sperm migration into the oviduct but not for the fertilization event. Moreover, the importance of primary sperm ZP binding, which has been thought to be a critical step in mammalian fertilization, should be reconsidered.

Mouse sperm undergo GPI-anchored protein release associated with lipid raft reorganization and acrosome reaction to acquire fertility

Mammalian sperm undergo several maturation steps after leaving the testis to become competent for fertilization. Important changes occur in sperm within the female reproductive tract, although the molecular mechanisms underlying these processes remain unclear. To investigate sperm membrane remodeling upon sperm maturation, we developed transgenic mouse lines carrying glycosylphosphatidylinositol (GPI)-anchored enhanced green fluorescent protein (EGFP–GPI) and traced the fate of this fluorescent protein during the fertility-acquiring process in sperm in vitro and in vivo. When the GFP-labeled sperm were treated with compounds for promoting the acrosome reaction, EGFP–GPI was released from the sperm surface crosslinked with characteristic relocation of a lipid raft marker ganglioside GM1. Sperm ejaculated into the uterus strongly expressed EGFP–GPI in the head region, whereas a part of the oviductal sperm lost fluorescence in a manner that was dependent on the presence of angiotensin-converting enzyme (ACE). Moreover, sperm on the zona pellucida of eggs in the oviduct were all found to have low levels of GFP. These results suggest that sperm undergoing GPI-anchored protein release associated with reorganization of lipid rafts and the acrosome reaction acquire fertilization potential.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Identification and disruption of sperm-specific angiotensin converting enzyme-3 (ACE3) in mouse

BACKGROUND

IZUMO1 is the only sperm protein which is proven to be essential for sperm-egg fusion. However, the IZUMO1 is a structurally simple protein with single Ig domain and seems not to include either a "fusogenic peptide" or a fusion machinery domain. This led us to assume the existence of an IZUMO1-interacting protein(s) which makes a functional fusion machine interacting with IZUMO1.

METHODOLOGY/PRINCIPAL FINDINGS

We produced a transgenic mouse line which expresses His-tagged IZUMO1 in the Izumo1(-/-) genetic background. After solubilization of sperm membranes, we purified His-tagged IZUMO1 using anti-His affinity chromatography and found a protein that interacts with IZUMO1. After being separated on SDS-PAGE gel, the IZUMO1-interacting protein was subjected to LC-MS/MS analysis and from the partial fragments, we identified the protein as ACE3. We raised the antibody against ACE3 and found that ACE3 is localized on the acrosomal cap area as in the case of IZUMO1. However, ACE3 disappeared from sperm after acrosome reaction while IZUMO1 remained on sperm. In order to investigate the role of ACE3 in vivo, we generated Ace3-deficient mice by homologous recombination and examined the fertilizing ability of the males. Unexpectedly, the male mice showed no defect in fertilizing ability in in vivo or in an in vitro fertilization system.

CONCLUSIONS/SIGNIFICANCE

We identified an IZUMO1-interacting protein in sperm, which we identified as testis specific ACE homologue ACE3. We produced an Ace3 disrupted mouse line, and found the localization of IZUMO1 spread in a little wider area on sperm, but the elimination of ACE3 did not result in a loss of sperm fertilizing ability, differing from the case of ACE disruption.

The role of angiotensin-(1-7) receptor Mas in spermatogenesis in mice and rats

Evidence regarding the components of the renin-angiotensin (Ang) system suggests that this system plays an important role in male reproduction. However, there are few data available in the literature on the effects of Ang-(1-7) on the male reproductive system. The present study investigated the effects of the genetic deletion and chronic blockage of Ang-(1-7) receptor Mas on spermatogenesis and male fertility. The localization of Mas in mouse and rat testes was determined by binding assays and immunofluorescence, whereas the testis structure and spermatogenic process were morphologically and stereologically analysed by light microscopy. Ang-(1-7) binding and immunofluorescence revealed the presence of Mas in the testes of mice and rats. Although the total numbers of Sertoli and Leydig cells per testis and Leydig cell size were similar in both wild-type and Mas-deficient mice, Mas(-/-) animals exhibited a significant reduction in testis weight and a greater volume of apoptotic cells, giant cells and vacuoles in the seminiferous epithelium. In both mice and rats, an increased number of apoptotic cells were found during meiosis. Due to disturbed spermatogenesis, daily sperm production was markedly reduced in Mas(-/-) mice. Moreover, chronic infusion of A-779 [an Ang-(1-7) antagonist] in rats significantly increased the total number of apoptotic cells and primary spermatocytes in particular stages of spermatogenesis. Taken together, these findings strongly suggest that Ang-(1-7) receptor Mas plays an important role in the regulation of spermatogenesis.

Interaction of angiotensin-converting enzyme (ACE) with membrane-bound carboxypeptidase M (CPM) - a new function of ACE

Angiotensin-converting enzyme (ACE) demonstrates, besides its typical dipeptidyl-carboxypeptidase activity, several unusual functions. Here, we demonstrate with molecular, biochemical, and cellular techniques that the somatic wild-type murine ACE (mACE), stably transfected in Chinese Hamster Ovary (CHO) or Madin-Darby Canine Kidney (MDCK) cells, interacts with endogenous membranal co-localized carboxypeptidase M (CPM). CPM belongs to the group of glycosylphosphatidylinositol (GPI)-anchored proteins. Here we report that ACE, completely independent of its known dipeptidase activities, has GPI-targeted properties. Our results indicate that the spatial proximity between mACE and the endogenous CPM enables an ACE-evoked release of CPM. These results are discussed with respect to the recently proposed GPI-ase activity and function of sperm-bound ACE.

Testicular Angiotensin-converting enzyme with different glycan modification: characterization on glycosylphosphatidylinositol-anchored protein releasing and dipeptidase activities

We have previously found that the angiotensin-converting enzyme (ACE) carries GPI-anchored protein releasing activity (GPIase) as well as dipeptidase activity. Testicular ACE (tACE), the male germinal specific isozyme, plays a crucial role in male fertilization. The amino-terminal region of this isozyme is different from that of somatic isozyme (sACE) and contains potential O-linked glycosylation sites. By multiple mutagenesis after an in silico prediction, amino acid residues acquiring O-glycans were assigned. Both GPIase and dipeptidase activities were compared between O-glycan null mutant and wild-type molecules, but no differences were found. Furthermore, the wild-type tACE was produced in two different cells (COS7 and CHO) and its activities compared. The GPIase activity, but not dipeptidase, was apparently higher for CHO-derived molecule than COS7. Sensitivity to neuraminidase and O-glycosidase digestions and the profile of glycosylation were quite different between these two molecules. Moreover, serial digestions with neuraminidase and O-glycosidase have no influence on GPIase activity of both molecules, suggesting that the sialylation and the presence of O-glycan has no influence on tACE enzyme activities, while the set of glycans modulate GPIase activity.

Mapping of conformational mAb epitopes to the C domain of human angiotensin I-converting enzyme

Angiotensin I-converting enzyme (ACE, CD143) has two homologous domains, each having a functional active site. Fine epitope mapping of 8 mAbs to the C-terminal domain of human ACE was carried out using plate precipitation assays, mAbs' cross-reactivity with ACE from different species, site-directed mutagenesis, and antigen- and cell-based ELISAs. Almost all epitopes contained potential glycosylation sites. Therefore, these mAbs could be used to distinguish different glycoforms of ACE expressed in different tissues or cell lines. mAbs 1B8 and 3F10 were especially sensitive to the composition of the N-glycan attached to Asn 731; mAbs 2H9 and 3F11 detected the glycosylation status of the glycan attached to Asn 685 and perhaps Asn1162; and mAb 1E10 and 4E3 recognized the glycan on Asn 666. The epitope of mAb 1E10 is located at the N-terminal end of the C domain, close to the unique 36 amino acid residues of testicular ACE (tACE). Moreover, it binds preferentially to tACE on the surface of human spermatozoa and thus may find application as an immunocontraceptive drug. mAb 4E3 was the best mAb for quantification of ACE-expressing somatic cells by flow cytometry. In contrast to the other mAbs, binding of mAb 2B11 was not markedly influenced by ACE glycosylation or by the cell culture conditions or cell types, making this mAb a suitable reference antibody. Epitope mapping of these C-domain mAbs, particularly those that compete with N-domain mAbs, enabled us to propose a model of the two-domain somatic ACE that might explain the interdomain cooperativity. Our findings demonstrated that mAbs directed to conformational epitopes on the C-terminal domain of human ACE are very useful for the detection of testicular and somatic ACE, quantification using flow cytometry and ELISA assays, and for the study of different aspects of ACE biology.